Avaliação do planejamento de prótese parcial removível em modelos recebidos por laboratórios de João Pessoa-PB

Objective: To evaluate the planning and quality of plaster models for fabricati on of removable parti al dentures received from three commercial prosthodonti c laboratories located in the city of João Pessoa, PB, Brazil, which perform the casting procedures in their facilities. Methods: Forty 40 plaster models were photographed per laboratory, totalizing 120 models. The evaluation was performed using two questi onnaires, one designed for the dental prosthesis technicians, and another applied by the investigator for the visual evaluati on of the models. Data were analyzed using the SPSS soft ware version 13.0. Results: Ninety-two (76.7%) models did not present planning. In addition, no model presented references of insertion plane or guide pins. Calculati on of the mouth preparati on index (MPI) to evaluate the distribution of the oclusal and cingulum abutments or rests showed that 86 (71.7%) models were classifi ed as poor, 23 (19.2%) models as good and only 11 (9,.2%) models as acceptable. Defects were found in 102 (85%) models. Conclusion: The prosthodontists are not preparing the mouth of their pati ents, neglecti ng the planning of removable partial dentures, and passing this responsibility to the dental prosthesis technicians. In addition, the quality of the models sent to the laboratories was unsatisfactory.

Designing for Safety : Implications of a Fifteen Year Review of Swallowed and Aspirated Dentures

Peer reviewed

MRI Registration for Human Hip Kinematics

Measurement of joint kinematics can provide knowledge to help improve joint prosthesis design, as well as identify joint motion patterns that may lead to joint degeneration or injury. More investigation into how the hip translates in live human subjects during high amplitude motions is needed. This work presents a design of a non-invasive method using the registration between images from conventional Magnetic Resonance Imaging (MRI) and open MRI to calculate three dimensional hip joint kinematics. The method was tested on a single healthy subject in three different poses. MRI protocols for the conventional gantry, high-resolution MRI and the open gantry, lowresolution MRI were developed. The scan time for the low-resolution protocol was just under 6 minutes. High-resolution meshes and low resolution contours were derived from segmentation of the high-resolution and low-resolution images, respectively. Low-resolution contours described the poses as scanned, whereas the meshes described the bones’ geometries. The meshes and contours were registered to each other, and joint kinematics were calculated. The segmentation and registration were performed for both cortical and sub-cortical bone surfaces. A repeatability study was performed by comparing the kinematic results derived from three users’ segmentations of the sub-cortical bone surfaces from a low-resolution scan. The root mean squared error of all registrations was below 1.92mm. The maximum range between segmenters in translation magnitude was 0.95mm, and the maximum deviation from the average of all orientations was 1.27◦. This work demonstrated that this method for non-invasive measurement of hip kinematics is promising for measuring high-range-of-motion hip motions in vivo.

Ceramic-veneered zirconia frameworks in full-arch implant rehabilitations: A 6-month to 5-year retrospective cohort study

Purpose: This was a retrospective cohort study designed to evaluate the clinical performance of ceramicveneered zirconia frameworks. Materials and Methods: Patients were recruited according to defined inclusion criteria. All patients were checked every 4 months from the time of definitive rehabilitation. At the end of 2013, all patients were rescheduled and rechecked for study purposes. The restorative procedures assessment was performed by previously established methods. The primary outcomes were the survival and success rates of the prosthesis. Descriptive statistics were used for the patient's demographics, implant distribution, and occurrence of complications. To study the survival and success of the prostheses, a Cox Regression analysis was used with a model constructed in a forward conditional stepwise mode. Predictive variables were included in the model, and adjusted survival curves were obtained for each outcome. Results: From 2008 to 2013, 75 patients were rehabilitated with 92 implant-supported, screw-retained, full-arch ceramic-veneered zirconia framework rehabilitations. The range of follow-up was between 6 months and 5 years. From the 92 full implant-supported screw-retained full-arch rehabilitations, Cox regression analysis indicated that within a 5-year time frame, the probability of framework fracture, major chipping, minor chipping, or any of the former combined to occur was 17.6%, 46.5%, 69.2%, and 90.5%, respectively. Conclusion: Results suggest zirconia as a suitable material for framework structure in implant-supported, full-arch rehabilitations. However, it experiences a high incidence of technical complications, mainly due to ceramic chipping. Further clinical studies should aim to ascertain the effects of clinical features and manufacturing procedures on the survival rates of these prostheses. © 2016 by Quintessence Publishing Co Inc.

Optimising the design and manufacture of a customised, prescription fit, Maxillo-facial prosthesis

This thesis is a continuation of the Enterprise-Ireland Research Innovation Fund (RIF) Project entitled’ "Design and Manufacturing of Customised Maxillo-Facial Prostheses" The primary objective of this Internal Research Development Program (IRDP) project was to investigate two fundamental design changes 1 To incorporate the over-denture abutments directly into the implant. 2 To remove the restraining wings by the addition of screws, which affix the. implant to the dense material of the jawbone. The prosthetic was redesigned using the ANSYS Finite Element Analysis software program and analysed to* • Reduce the internal von Mises stress distribution The new prosthetic had a -63.63 % lower von Mises stress distribution when compared with the original prosthetic. • Examine the screw preload effects. A maximum relative displacement of 22 6 * lO^mm between the bone and screw was determined, which is well below the critical threshold of micromotion which prevents osseointegration • Investigate the prosthetic-bone contact interface. Three models of the screw, prosthesis, and bone, were studied. (Axisymmetnc, quarter volume, and full volume), a recommended preload torque of 0 32 Nm was applied to the prosthetic and a maximum von Mises stress of 1.988 MPa was predicted • Study the overdenture removal forces. This analysis could not be completed because the correct plastic multilinear properties of the denture material could not be established The redesigned prosthetic was successfully manufactured on a 3-axis milling machine with an indexing system The prosthetic was examined for dimensional quality and strength The research established the feasibility of the new design and associated manufacturing method.

Development of musculoskeletal models for the design and the pre-clinical validation of hip resurfacing prosthesis

Background. The surgical treatment of dysfunctional hips is a severe condition for the patient and a costly therapy for the public health. Hip resurfacing techniques seem to hold the promise of various advantages over traditional THR, with particular attention to young and active patients. Although the lesson provided in the past by many branches of engineering is that success in designing competitive products can be achieved only by predicting the possible scenario of failure, to date the understanding of the implant quality is poorly pre-clinically addressed. Thus revision is the only delayed and reliable end point for assessment. The aim of the present work was to model the musculoskeletal system so as to develop a protocol for predicting failure of hip resurfacing prosthesis. Methods. Preliminary studies validated the technique for the generation of subject specific finite element (FE) models of long bones from Computed Thomography data. The proposed protocol consisted in the numerical analysis of the prosthesis biomechanics by deterministic and statistic studies so as to assess the risk of biomechanical failure on the different operative conditions the implant might face in a population of interest during various activities of daily living. Physiological conditions were defined including the variability of the anatomy, bone densitometry, surgery uncertainties and published boundary conditions at the hip. The protocol was tested by analysing a successful design on the market and a new prototype of a resurfacing prosthesis. Results. The intrinsic accuracy of models on bone stress predictions (RMSE < 10%) was aligned to the current state of the art in this field. The accuracy of prediction on the bone-prosthesis contact mechanics was also excellent (< 0.001 mm). The sensitivity of models prediction to uncertainties on modelling parameter was found below 8.4%. The analysis of the successful design resulted in a very good agreement with published retrospective studies. The geometry optimisation of the new prototype lead to a final design with a low risk of failure. The statistical analysis confirmed the minimal risk of the optimised design over the entire population of interest. The performances of the optimised design showed a significant improvement with respect to the first prototype (+35%). Limitations. On the authors opinion the major limitation of this study is on boundary conditions. The muscular forces and the hip joint reaction were derived from the few data available in the literature, which can be considered significant but hardly representative of the entire variability of boundary conditions the implant might face over the patients population. This moved the focus of the research on modelling the musculoskeletal system; the ongoing activity is to develop subject-specific musculoskeletal models of the lower limb from medical images. Conclusions. The developed protocol was able to accurately predict known clinical outcomes when applied to a well-established device and, to support the design optimisation phase providing important information on critical characteristics of the patients when applied to a new prosthesis. The presented approach does have a relevant generality that would allow the extension of the protocol to a large set of orthopaedic scenarios with minor changes. Hence, a failure mode analysis criterion can be considered a suitable tool in developing new orthopaedic devices.

An Electromagnetic Tracker System for the design of a dental superstructure

Nowadays, different techniques are available for manufacturing full-arch implant-supported prosthesis, many of them based on an impression procedure. Nevertheless, the long-term success of the prosthesis is highly influenced by the accuracy during such process, being affected by factors such as the impression material, implant position, angulation and depth. This paper investigates the feasibility of a 3D electromagnetic motion tracking system as an acquisition method for modeling such prosthesis. To this extent, we propose an implant acquisition method at the patient mouth, using a specific prototyped tool coupled with a tracker sensor, and a set of calibration procedures (for distortion correction and tool calibration), that ultimately obtains combined measurements of the implant’s position and angulation, and eliminating the use of any impression material. However, in the particular case of the evaluated tracking system, the order of magnitude of the obtained errors invalidates its use for this specific application.

Electromagnetic tracker feasibility in the design of a dental superstructure for edentulous patients

The success of the osseointegration concept and the Brånemark protocol is highly associated to the accuracy in the production of an implant-supported prosthesis. One of most critical steps for long-term success of these prosthesis is the accuracy obtained during the impression procedure, which is affected by factors such as the impression material, implant position, angulation and depth. This paper investigates the feasibility of 3D electromagnetic motion tracking systems as an acquisition method for modeling full-arch implant-supported prosthesis. To this extent, we propose an implant acquisition method at the patient mouth and a calibration procedure, based on a 3D electromagnetic tracker that obtains combined measurements of implant’s position and angulation, eliminating the use of any impression material. Three calibration algorithms (namely linear interpolation, higher-order polynomial and Hardy multiquadric) were tested to compensate for the electromagnetic tracker distortions introduced by the presence of nearby metals. Moreover, implants from different suppliers were also tested to study its impact on tracking accuracy. The calibration methodology and the algorithms employed proved to implement a suitable strategy for the evaluation of novel dental impression techniques. However, in the particular case of the evaluated electromagnetic tracking system, the order of magnitude of the obtained errors invalidates its use for the full-arch modeling of implant-supported prosthesis.

Design of a bifurcated stent graft, with its accompanying delivery system.

Abdominal Aortic Aneurysms (AAA) haemorhaging is a life-threatening disease. An aneurysm is a permanent swelling of an artery due to a weakness in its wall. Current surgical repair involves opening the chest or abdomen, gaining temporary vascular control of the aorta and suturing a prosthetic graft to the healthy aorta within the aneurysm itself The outcome of this surgical approach is not perfect, and the quality of life after this repair is impaired by postoperative pain, sexual dysfunction, and a lengthy hospital stay resulting in high health costs. All these negative effects are related to the large incision and extensive tissue dissection. Endovascular grafting is an alternative to the standard surgical method. This treatment is a less invasive method of treating aortic aneurysms. It involves a surgical exposure of the common femoral arteries where the stent graft can be inserted through by an over-the-wire technique. All manipulations are controlled from a remote place by the use of a catheter and this technique avoids the need to directly expose the diseased artery through a large incision or an extensive dissection. The proposed design method outlined in this project is to develop the endovascular approach. The main aim is to design an unitary bifurcated stent graft (1 e- bifurcated graft as a single component) to treat these Abdominal Aortic Aneurysms. This includes the delivery system and deployment mechanism necessary to first accurately position the stent graft across the aneurysm sac and also across the iliac bifurcation, and secondly fix the stent graft in position by using expandable metal stents. Thus, excluding the aneurysm from the circulation and therefore preventing rupture. Miniaturisation is a critical aspect of this design, as the smaller the crimped stent graft the easier to guide through the vascular system to the desired location. Biocompatibility is an important aspect. The preferred materials for this prosthesis are to use Shape Memory Alloys for the stent and a multifilament fabric for the graft. A taper design is applied for the geometry as this gives a favourable flow characteristic and reduced wave reflections. Adequate testing of the stent graft to prove its durability and the ease of the method of deployment is a prerequisite. A bench test facility has being designed and build to replicate the cardiovascular system and the disease in question aortic aneurysms at the iliac bifurcation. The testing here shows the feasibility of the proposed delivery system and the durability of the stent graft across the aneurysm sac. Finally, these endovascular treatments offer the economic advantage of short hospital stays or even treatment as an outpatient, as well as elimination of the need for postoperative intensive care The risk of developing an aneurysm increases with age, that is one of the mam reasons to look for less invasive ways of treating aneurysms. Consequently, there is enormous pressure to develop and use these devices rapidly.

Tightening force and torque of nonlocking screws in a reverse shoulder prosthesis.

BACKGROUND: Reversed shoulder arthroplasty is an accepted treatment for glenohumeral arthritis associated to rotator cuff deficiency. For most reversed shoulder prostheses, the baseplate of the glenoid component is uncemented and its primary stability is provided by a central peg and peripheral screws. Because of the importance of the primary stability for a good osteo-integration of the baseplate, the optimal fixation of the screws is crucial. In particular, the amplitude of the tightening force of the nonlocking screws is clearly associated to this stability. Since this force is unknown, it is currently not accounted for in experimental or numerical analyses. Thus, the primary goal of this work is to measure this tightening force experimentally. In addition, the tightening torque was also measured, to estimate an optimal surgical value. METHODS: An experimental setup with an instrumented baseplate was developed to measure simultaneously the tightening force, tightening torque and screwing angle, of the nonlocking screws of the Aquealis reversed prosthesis. In addition, the amount of bone volume around each screw was measured with a micro-CT. Measurements were performed on 6 human cadaveric scapulae. FINDINGS: A statistically correlated relationship (p<0.05, R=0.83) was obtained between the maximal tightening force and the bone volume. The relationship between the tightening torque and the bone volume was not statistically significant. INTERPRETATION: The experimental relationship presented in this paper can be used in numerical analyses to improve the baseplate fixation in the glenoid bone.

Soft tissue artifact distribution on lower limbs during treadmill gait: Influence of skin markers' location on cluster design.

Segment poses and joint kinematics estimated from skin markers are highly affected by soft tissue artifact (STA) and its rigid motion component (STARM). While four marker-clusters could decrease the STA non-rigid motion during gait activity, other data, such as marker location or STARM patterns, would be crucial to compensate for STA in clinical gait analysis. The present study proposed 1) to devise a comprehensive average map illustrating the spatial distribution of STA for the lower limb during treadmill gait and 2) to analyze STARM from four marker-clusters assigned to areas extracted from spatial distribution. All experiments were realized using a stereophotogrammetric system to track the skin markers and a bi-plane fluoroscopic system to track the knee prosthesis. Computation of the spatial distribution of STA was realized on 19 subjects using 80 markers apposed on the lower limb. Three different areas were extracted from the distribution map of the thigh. The marker displacement reached a maximum of 24.9mm and 15.3mm in the proximal areas of thigh and shank, respectively. STARM was larger on thigh than the shank with RMS error in cluster orientations between 1.2° and 8.1°. The translation RMS errors were also large (3.0mm to 16.2mm). No marker-cluster correctly compensated for STARM. However, the coefficient of multiple correlations exhibited excellent scores between skin and bone kinematics, as well as for STARM between subjects. These correlations highlight dependencies between STARM and the kinematic components. This study provides new insights for modeling STARM for gait activity.

Removable Partial Denture in Combination with a Milled Fixed Partial Prosthesis as Interim Restorations in Long-Term Treatment

Interim restorations are frequently used in prosthodontic treatments. Many complex situations require the combination of fixed and removable partial prostheses. An appropriate interim restoration design that accurately implements the treatment plan is necessary to prepare the oral cavity for the prostheses, and to contribute to the preservation and health of remaining natural teeth, bone support, and gingival tissues. This report describes a modified technique for construction of interim restorations with a combination of fixed and removable partial prostheses. The technique consists of the construction of a milled fixed prosthesis and removable partial denture with metallic framework for use during extensive treatment, improving masticatory function and esthetics and preserving the periodontal health of supporting structures. This interim restoration can also serve as a template for the definitive restoration, allowing patient and dentist to evaluate appearance and function and helping to ensure the success of the definitive restoration.

Stress distribution in implant-supported prosthesis with external and internal implant-abutment connections

Objective. This study aimed to investigate the stress distribution in screwed implant-supported prostheses with different implant-abutment connections by using a photoelastic analysis. Materials and methods. Four photoelastic models were fabricated in PL-2 resin and divided according to the implant-abutment connection (external hexagon (EH) and Morse taper (MT) implants (3.75 × 11.5 mm)) and the number crowns (single and 3-unit piece). Models were positioned in a circular polariscope and 100-N axial and oblique (45) loading were applied in the occlusal surface of the crowns by using a universal testing machine. The stresses were photographically recorded and qualitatively analyzed using software (Adobe Photoshop). Results. Under axial loading, the MT implants exhibited a lower number of fringes for single-unit crowns than EH implants, whereas for a 3-unit piece the MT implants showed a higher number of fringes vs EH implants. The oblique loading increased the number of fringes for all groups. Conclusion. In conclusion, the MT implant-abutment connection reduced the amount of stress in single-unit crowns, for 3-unit piece crowns the amount of stress was lower using an external hexagon connection. The stress pattern was similar for all groups. Oblique loading promoted a higher stress concentration than axial loading. © Informa Healthcare.

Comparison of different designs of implant-retained overdentures and fixed full-arch implant-supported prosthesis on stress distribution in edentulous mandible - A computed tomography-based three-dimensional finite element analysis

A finite element analysis was used to compare the effect of different designs of implant-retained overdentures and fixed full-arch implant-supported prosthesis on stress distribution in edentulous mandible. Four models of an human mandible were constructed. In the OR (O'ring) group, the mandible was restored with an overdenture retained by four unsplinted implants with O'ring attachment; in the BC (bar-clip) -C and BC groups, the mandibles were restored with overdentures retained by four splinted implants with bar-clip anchor associated or not with two distally placed cantilevers, respectively; in the FD (fixed denture) group, the mandible was restored with a fixed full-arch four-implant-supported prosthesis. Models were supported by the masticatory muscles and temporomandibular joints. A 100-N oblique load was applied on the left first molar. Von Mises (σvM), maximum (σmax) and minimum (σmin) principal stresses (in MPa) analyses were obtained. BC-C group exhibited the highest stress values (σvM=398.8, σmax=580.5 and σmin=-455.2) while FD group showed the lowest one (σvM=128.9, σmax=185.9 and σmin=-172.1). Within overdenture groups, the use of unsplinted implants reduced the stress level in the implant/prosthetic components (59.4% for σvM, 66.2% for σmax and 57.7% for σmin versus BC-C group) and supporting tissues (maximum stress reduction of 72% and 79.5% for σmax, and 15.7% and 85.7% for σmin on the cortical and trabecular bones, respectively). Cortical bone exhibited greater stress concentration than the trabecular bone for all groups. The use of fixed implant dentures and removable dentures retained by unsplinted implants to rehabilitate edentulous mandible reduced the stresses in the periimplant bone tissue, mucosa and implant/prosthetic components. © 2013 Elsevier Ltd.

Influence of abutment-to-fixture design on reliability and failure mode of all-ceramic crown systems

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)